1. Field of the Invention
This invention relates to a liquid recording material to be used for various writing implements or a so called ink-jet recording device, particularly to a liquid recording material which is suitable for use in the latter ink-jet recording device.
2. Description of the Prior Art
There have herertofore been used liquid recording materials (hereinafter referred to as "ink"), containing various dyes dissolved in water or other organic solvents, for use in performing writing on a material to be recorded such as paper with a writing implement (e.g. fountain pen, felt pen, etc.).
Also, in a so called ink-jet recording system, wherein recording is effected by discharging a liquid in a recording head through a discharge orifice by the force of oscillation of a piezoelectric oscillator or electrostatic attraction by application of a high voltage, it is known to use a composition having various dyes dissolved in water or an organic solvent. But, as compared with inks for writing implements such as fountain pen or felt pen, more severe conditions in various aspects of characteristics are required for an ink for an ink-jet recording system.
The ink-jet recording method enables high speed recording or color recording on a plain paper without specific fixing treatment with little emission of noise, and various systems therefor have actively been developed.
In such an ink-jet recording method, droplets of ink are generated based on various principles and deposited on a material to effect recording. And, such an ink comprises as essential components a recording agent (for which a dye or a pigment is used) and a liquid vehicle (for which water, various organic solvents or mixtures thereof are used), optionally containing various additives.
In this connection, the ink-jet recording method may be classified into various systems depending on the method for generation of ink droplets and the method for controlling the flight direction of ink droplets. One example is shown in FIG. 1.
Namely, the device as shown in FIG. 1 performs recording by giving a recording signal to the recording head section having a piezoelectric oscillator and generating ink droplets corresponding to said signal. In FIG. 1, numeral 1 is a recording head, having a piezooscillator 2a, a vibration board 2b, an inlet 3 for ink, a liquid chamber 4 in head and discharge outlet (discharge orifice) 5. Into the liquid chamber 4, an ink 7 stored in a storage tank 6 is introduced through a supplying pipe 8. In some cases, somewhere along the supplying pipe 8, there may also be provided an intermediate treatment means 9 such as a pump or a filter. And, on the piezoelectric oscillator 2a, a signal converted to a pulse from the recording signal S by means of a signal treating means (e.g. pulse convertor) 10 is applied, whereby a pressure change is incurred on the ink in the liquid chamber 4. As a result, the ink 7 is discharged as droplets 11 through the discharge orifice 5 thereby to effect recording on the surface of a material to be recorded 12.
Other than the device as described above, various types of devices are known. For example, as shown in FIG. 2, there is a modification of the device as shown in FIG. 1, wherein the liquid chamber 4 is shaped in a nozzle and a cylindrical piezoelectric oscillator is arranged around the outer peripheral portion thereof (the mechanism for generation of ink droplets is essentially the same as in the device as shown in FIG. 1). There is also known another device in which charged droplets are continuously generated and a part of said droplets are used for recording, or alternatively a device in which heat energy corresponding to the recording signal is given to the ink in the chamber of recording head, and liquid droplets are formed by said energy.
An embodiment of such a device is shown in FIG. 3A, FIG. 3B and FIG. 4.
The head 13 can be obtained by bonding a plate of glass, ceramics or plastic having a channel 14 for passing ink to a heat generating head 15 to be used for heat sensitive recording (in the drawing, a thin film head is shown, but the head is not limited thereto). The head 15 is constituted of a protective film 16 formed of silicon oxide, etc., aluminum electrodes 17-1, 17-2, a heat generating resistor layer 18 formed of nickel-chromium, etc., a heat accumulating layer 19 and a substrate with good heat dissipation such as alumina, etc.
The ink 21 comes up to the discharge orifice 22, and forms a meniscus 23 by the pressure P.
Now, on application of an electric signal across the electrodes 17-1 and 17-2, heat generation occurs abruptly at the portion indicated by n in the heat generating head 15 to form bubbles of the ink contacted at said portion. By the pressure of the bubbles, the meniscus 23 is protruded to discharge the ink 21 which flights through the orifice 22 as small droplets 24 toward the material to be recorded 25. In FIG. 4, there is shown an exterior view of a multi-head in which a number of heads as shown in FIG. 3A are arranged. Said multi-head is prepared by bonding a glass plate 27 having a multi-channel 26 to a heat generating head 28 similar to that described with reference to FIG. 3A.
As described above, among the devices defined comprehensively for effecting recording by flight of ink droplets, there are included various methods for generation of ink droplets and for controlling the flight direction of ink droplets. Therefore, for the purpose of performing good recording, the ink to be employed is required to have physical property values such as viscosity, surface tension and specific resistivity corresponding to the method for generation of ink droplets or the method for controlling the flight direction of ink droplets. And, in any of the systems, the ink employed is required to form no solid by vaporization of the liquid vehicle or chemical changes of the constituents during a long term storage or intermission of recording. Generally speaking, the discharge orifice in a ink-jet system recording device is a minute hole (having generally a diameter of some 10 microns) and therefore clogging may be caused by generation of solids and sometimes no ink droplet can be discharged.
Even if cessation of discharging does not occur, generation of solids will cause deleterious affects on generation of uniform ink droplets or stable flight of ink droplets, whereby recording performance, discharging stability, discharging response or continuous recordability may sometimes be lowered. Alternatively, when the constituents of ink undergo chemical changes, the physical properties adjusted to desired values at the time of preparation are changed, whereby recording performance, discharging stability or discharging response may also sometimes be lowered. Thus, it would be very desirable to have a liquid vehicle component difficulty vaporized, a chemically stable recording agent or a combination of a liquid vehicle and a recording agent free from the drawback as mentioned above.
Furthermore, the recorded image is also required to be sufficiently high in contrast and clear. Generally speaking, the inks of prior art tend to cause clogging of the discharge orifice, when the contrast of the recorded image is intended to be improved by increase of the content of a recording agent. Accordingly, it is earnestly desired to have a recording agent which is highly soluble in a liquid vehicle and has a clear tone.
In addition to the above characteristics, it is also required for the ink to be capable of recording without restriction as to the material to be recorded, to be high in fixing speed, to give an image excellent in water resistance, light resistance, friction resistance and resolution, and to be free from odor.
In view of the above points, there have been made various proposals concerning inks, but substantially no practical ink satisfying all of the above conditions has yet been obtained.